Presentation on theme: "Atmospheric Variability Why is it so cold winter 2010-2011? Why was it so hot summer 2010? Why was it so dry in 2007? Why was it so wet in 1998, 2009 (fall)?"— Presentation transcript:
Atmospheric Variability Why is it so cold winter 2010-2011? Why was it so hot summer 2010? Why was it so dry in 2007? Why was it so wet in 1998, 2009 (fall)? Are these extremes becoming more common? Why or why not? Does variability in atmospheric flow patterns fully answer these questions?
What is a teleconnection AMS: 1. A linkage between weather changes occurring in widely separated regions of the globe. 2. A significant positive or negative correlation in the fluctuations of a field at widely separated points. Most commonly applied to variability on monthly and longer timescales, the name refers to the fact that such correlations suggest that information is propagating between the distant points through the atmosphere.” Pressure fluctuations SST Height anomalies (700, 500mb) Associations with circulation indices
The North Atlantic Oscillation (NAO) Pressure dipole in North Atlantic centered near Iceland/Greenland and over the Azores Icelandic Low vs Azores High Tendency for either both weak or both strong Dominant mode of Variability in Atlantic Winter The NAO index is obtained by projecting the NAO loading pattern to the daily anomaly 500 millibar height field over 0- 90°N. The NAO loading pattern has been chosen as the first mode of a Rotated Empirical Orthogonal Function (EOF) analysis using monthly mean 500 millibar height anomaly data from 1950 to 2000 over 0-90°N latitude. (NCDC)
Arctic Oscillation (AO) or NHam Cyclonic circulation of upper level winds around the Arctic Latitude poleward of 55°N Positive = stronger winds- confines Arctic air More zonal Negative = relaxed winds- Arctic air oozes southward AO index is obtained by projecting the AO loading pattern to the daily anomaly 1000 millibar height field over 20°N-90°N latitude
Pacific North American (PNA) Quadripole pattern of 500mb height anomalies All months except June and July winter Center locations Similar signs south of Aleutians and over SE U.S. Hawaii and InterMountain U.S. and Canada The PNA index is obtained by projecting the PNA loading pattern to the daily anomaly 500 millibar height field over 0- 90°N. The PNA loading pattern has been chosen as the second mode of a Rotated EOF analysis using monthly mean 500 millibar height anomaly data from 1950 to 2000 over 0-90°N latitude.
El Nino Southern Oscillation (ENSO) Both a SST and pressure fluctuation in the tropical Pacific ~ 5-7 year periodicity Most significant atmospheric/oceanic coupling in the world El Nino = warmer than normal SST La Nina = colder than normal SST Southern oscillation= pressure flip-flop http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/sstanim.shtml
Southern Oscillation Index (SOI) Standardized difference in MSLP between Darwin Australia and Tahiti (T-D) Pressure normally higher over Tahiti and lower over Darwin Slow east to west flow of tropical water
Discovered 1996 (Hare and Mantua) Leading principal component of Northern Pacific SST variability Similar to ENSO Long-lived ENSO Greater SST variability in mid latitiude Pacific Pacific Decadal Oscillation (PDO)
Table 1: summary of North American climate anomalies associated with extreme phases of the PDO. climate anomaliesWarm Phase PDOCool Phase PDO Ocean surface temperatures in the northeastern and tropical Pacific Above averageBelow average October-March northwestern North American air temperatures Above averageBelow average October-March Southeastern US air temperatures Below averageAbove average October-March southern US/Northern Mexico precipitation Above averageBelow average October-March Northwestern North America and Great Lakes precipitation Below averageAbove average Northwestern North American spring time snow pack Below averageAbove average Winter and spring time flood risk in the Pacific Northwest Below averageAbove average
Atlantic Multidecadal Oscillation (AMO) Fluctuation in detrended SST in north Atlantic (0 – 70°N) AMO index 10 year running mean Relationships to speed of thermohaline circulation
Quasi Biennial Oscillation (QBO) Oscillating (E-W) stratospheric winds 10 – 100 mb above the equator 20 – 36 month periodicity Impacts Spike in ATL hurricane activity during west (positive) zonal flow May impact Asian monsoon and ENSO
MJO and Atlantic Hurricanes Phase 1 and 2 support a more active regime of Atlantic convection ACE > 76 91.5 major hurricane days (1974 – 2007) Phase 6 and 7 less active ACE < 36 20.5 major hurricane days (1974 – 2007)
Others not discussed ESRL Indices http://www.esrl.noaa.gov/psd/data/climateindi ces/list/ http://www.esrl.noaa.gov/psd/data/climateindi ces/list/ Climate Prediction Center http://www.cpc.ncep.noaa.gov/